Two-dimensional free-space optical wavelength routing element based on stepwise controlled tilting mirrors

ABSTRACT

A microstructure for steering light is provided that may be stepwise controlled to provide tilt positions in two dimensions. The arrangement is two-dimensional since a tilt axis may be defined as the axis along which the base is tilted to move from one of the two tilt positions to the other. At least one additional tilt position is provided that cannot be reached from either of those two tilt positions by tilting the micromirror assembly along the tilt axis. Instead, such an additional tilt position requires that there at least be a tilt component in a direction orthogonal to the tilt axis.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is being filed concurrently with related U.S. patentapplication 09/899,000 “FREE-SPACE OPTICAL WAVELENGTH ROUTING ELEMENTBASED ON STEPWISE CONTROLLED TILTING MIRRORS” by Victor Buzzetta, BevanStaple, and David Marinelli, which is herein incorporated by referencein its entirety for all purposes.

BACKGROUND OF THE INVENTION

This application relates generally to optical routing and morespecifically to microelectromechanical systems for routing opticalsignals.

The Internet and data communications are causing an explosion in theglobal demand for bandwidth. Fiber optic telecommunications systems arecurrently deploying a relatively new technology called dense wavelengthdivision multiplexing (DWDM) to expand the capacity of new and existingoptical fiber systems to help satisfy this demand. In DWDM, multiplewavelengths of light simultaneously transport information through asingle optical fiber. Each wavelength operates as an individual channelcarrying a stream of data. The carrying capacity of a fiber ismultiplied by the number of DWDM channels used. Today DWDM systemsemploying up to 80 channels are available from multiple manufacturers,with more promised in the future.

In all telecommunication networks, there is the need to connectindividual channels (or circuits) to individual destination points, suchas an end customer or to another network. Systems that perform thesefunctions are called cross-connects. Additionally, there is the need toadd or drop particular channels at an intermediate point. Systems thatperform these functions are called add-drop multiplexers (ADMs). All ofthese networking functions are currently performed byelectronics—typically an electronic SONET/SDH system. However SONET/SDHsystems are designed to process only a single optical channel.Multi-wavelength systems would require multiple SONET/SDH systemsoperating in parallel to process the many optical channels. This makesit difficult and expensive to scale DWDM networks using SONET/SDHtechnology.

The alternative is an all-optical network. Optical networks designed tooperate at the wavelength level are commonly called “wavelength routingnetworks” or “optical transport networks” (OTN). In a wavelength routingnetwork, the individual wavelengths in a DWDM fiber must be manageable.New types of photonic network elements operating at the wavelength levelare required to perform the cross-connect, ADM and other networkswitching functions. Two of the primary functions are optical add-dropmultiplexers (OADM) and wavelength-selective cross-connects (WSXC).

In order to perform wavelength routing functions optically today, thelight stream must first be de-multiplexed or filtered into its manyindividual wavelengths, each on an individual optical fiber. Then eachindividual wavelength must be directed toward its target fiber using alarge array of optical switches commonly called an optical cross-connect(OXC). Finally, all of the wavelengths must be re-multiplexed beforecontinuing on through the destination fiber. This compound process iscomplex, very expensive, decreases system reliability and complicatessystem management. The OXC in particular is a technical challenge. Atypical 40-80-channel DWDM system will require thousands of switches tofully cross-connect all the wavelengths. Opto-mechanical switches, whichoffer acceptable optical specifications, are too big, expensive andunreliable for widespread deployment. New integrated solid-statetechnologies based on new materials are being researched, but are stillfar from commercial application.

Consequently, the industry is aggressively searching for an all-opticalwavelength routing solution that enables cost-effective and reliableimplementation of high-wavelength-count systems.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a microstructure for steering lightthat provides enhanced flexibility. The microstructure may be configuredto function as an optical switch for directing an optical signal from asingle input port to one of at least three output ports. Suchconfigurations may be adapted for use in a wavelength router.Alternatively, the flexibility of the microstructure may be used toachieve improved alignment so that the light-steering efficiency isimproved.

In one embodiment, a pivot member is connected with a structural filmand supports a base that includes a reflective coating. The reflectivecoating may comprise gold. The pivot member may be a post pivot. Atleast three noncollinear fixed rotational actuators are connected withthe structural film, each being configured to deflect the base towardsthe structural film upon activation. A movable hard stop connected withthe structural film may additionally be included in some embodiments. Inthat case, the base assumes one of a plurality of tilt positionsaccording to which of the fixed rotational actuators is activated andaccording to a position of the movable hard stop. The movable hard stopmay be linearly actuated. In certain embodiments, it comprises aplurality of discrete levels, each of which contacts the base in one ofthe tilt positions.

Some embodiments include a plurality of noncollinear such movable hardstops. In one embodiment, the number of movable hard stops is equal tothe number of fixed rotational actuators. In another embodiment, asubset of the movable hard stops are configured to move collinearly,such as by being connected with each other.

Further embodiments provide a method for steering light from an inputport to one of a plurality of output ports. A micromirror assembly istilted among at least three tilt positions that correspond to three ofthe output ports. The arrangement is two-dimensional in the followingsense. For any two tilt positions, a tilt axis may be defined as theaxis along which the micromirror assembly is tilted to move from one ofthe two tilt positions to the other. At least one additional tiltposition is provided that cannot be reached from either of those twotilt positions by tilting the micromirror assembly along the tilt axis.Instead, such an additional tilt position requires that there at leastbe a tilt component in a direction orthogonal to the tilt axis. Light isthen reflected off the micromirror assembly from the input port to oneof the output ports.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings wherein like reference numerals are usedthroughout the several drawings to refer to similar components. In someinstances, a sublabel is associated with a reference numeral and isenclosed in parentheses to denote one of multiple similar components.When reference is made to a reference numeral without specification toan existing sublabel, it is intended to refer to all such multiplesimilar components.

FIGS. 1A, 1B, and 1C are schematic top, side, and end views,respectively, of one embodiment of a wavelength router that usesspherical focusing elements;

FIGS. 2A and 2B are schematic top and side views, respectively, of asecond embodiment of a wavelength router that uses spherical focusingelements; and

FIG. 3 is a schematic top view of a third embodiment of a wavelengthrouter that uses spherical focusing elements;

FIGS. 4A and 4B are side and top views of an implementation of amicromirror retroreflector array;

FIG. 4C is a side view of a multiposition micromirror that may be usedas a 1×N switch;

FIGS. 5A-5C are cross-sectional drawings of a tilting micromirror inpositions effected by activation of different actuators;

FIGS. 6A, 6B, 6C, 6D, and 6E are cross-sectional drawings of oneembodiment of a multiposition tilting micromirror assembly using linearactuators;

FIGS. 7A, 7B, 7C, and 7D are cross-sectional drawings of an embodimentof a multiposition tilting micromirror assembly using a single linearactuator;

FIG. 7E is a top view of an embodiment of a multiposition tiltingmicromirror assembly using a single linear actuator;

FIGS. 8A, 8B, 8C, 8D, 8E, and 8F are cross-sectional drawings of afurther embodiment of a multiposition tilting micromirror assembly usinga single linear actuator; and

FIGS. 9A, 9B, 9C, 9D, 9E, and 9F are to views of multiposition tiltingmicromirror assemblies that have different configurations in twodimensions.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

1. Introduction

The following description sets forth embodiments of an optical routingelement. In some embodiments, the optical routing element may be used inan optical wavelength router. Accordingly, embodiments of the inventioncan be applied to network elements such as optical add-drop multiplexers(OADMs) and wavelength-selective cross-connects (WSXCs), among others,to achieve the goals of optical networking systems.

The general functionality of one optical wavelength router that can beused with the embodiments of the invention is described in detail in thecopending, commonly assigned U.S. patent application, filed Nov. 16,1999 and assigned Ser. No. 09/442,061, entitled “Wavelength Router,”which is herein incorporated by reference in its entirety, including theAppendix, for all purposes. As described therein, such an opticalwavelength router accepts light having a plurality of spectral bands atan input port and selectively directs subsets of the spectral bands todesired ones of a plurality of output ports. As used herein, the terms“input port” and “output port” are intended to have broad meanings. Atthe broadest, a port is defined by a point where light enters or leavesthe optical router. For example, the input (or output) port could be thelocation of a light source (or detector) or the location of thedownstream end of an input fiber (or the upstream end of an outputfiber).

The wavelength router thus includes a dispersive element, such as adiffraction grating or prism, which operates to deflect incoming lightby a wavelength-dependent amount. Different portions of the deflectedlight are intercepted by different routing elements. The InternationalTelecommunications Union (ITU) has defined a standard wavelength gridhaving a frequency band centered at 193,100 GHz, and another band atevery 100 GHz interval around 193,100 GHz. This corresponds to awavelength spacing of approximately 0.8 nm around a center wavelength ofapproximately 1550 nm, it being understood that the grid is uniform infrequency and only approximately uniform in wavelength. The ITU has alsodefined standard data modulation rates. The OC-48 modulation correspondsto approximately 2.5 GHz, OC-192 to approximately 10 GHz, and OC-768 toapproximately 40 GHz.

2. Wavelength Router Configurations

FIGS. 1A, 1B, and 1C are schematic top, side, and end views,respectively of one embodiment of a wavelength router 10. Its generalfunctionality is to accept light having a plurality N of spectral bandsat an input port 12, and to direct subsets of the spectral bands todesired ones of a plurality M of output ports, designated 15(1) . . .15(M). The output ports are shown in the end view of FIG. 1C as disposedalong a line 17 that extends generally perpendicular to the top view ofFIG. 1A. Light entering the wavelength router 10 from input port 12forms a diverging beam 18, which includes the different spectral bands.Beam 18 encounters a lens 20 that collimates the light and directs it toa reflective diffraction grating 25. The grating 25 disperses the lightso that collimated beams at different wavelengths are directed atdifferent angles back towards the lens 20.

Two such beams are shown explicitly and denoted 26 and 26′, the latterdrawn in dashed lines. Since these collimated beams encounter the lens20 at different angles, they are focused towards different points alonga line 27 in a transverse plane extending in the plane of the top viewof FIG. 1A. The focused beams encounter respective ones of a pluralityof retroreflectors, designated 30(1) . . . 30(N), located near thetransverse plane. The beams are directed back, as diverging beams, tothe lens 20 where they are collimated, and directed again to the grating25. On the second encounter with the grating 25, the angular separationbetween the different beams is removed and they are directed back to thelens 20, which focuses them. The retroreflectors 30 may be configured tosend their intercepted beams along a reverse path displaced alongrespective lines 35(1) . . . 35(N) that extend generally parallel toline 17 in the plane of the side view of FIG. 1B and the end view ofFIG. 1C, thereby directing each beam to one or another of output ports15.

Another embodiment of a wavelength router, designated 10′, isillustrated with schematic top and side views in FIGS. 2A and 2B,respectively. This embodiment may be considered an unfolded version ofthe embodiment of FIGS. 1A-1C. Light entering the wavelength router 10′from input port 12 forms diverging beam 18, which includes the differentspectral bands. Beam 18 encounters a first lens 20 a, which collimatesthe light and directs it to a transmissive grating 25′. The grating 25′disperses the light so that collimated beams at different wavelengthsencounter a second lens 20 b, which focuses the beams. The focused beamsare reflected by respective ones of plurality of retroreflectors 30 asdiverging beams, back to lens 20 b, which collimates them and directsthem to grating 25′. On the second encounter, the grating 25′ removesthe angular separation between the different beams, which are thenfocused in the plane of output ports 15 by lens 20 a.

A third embodiment of a wavelength router, designated 10″, isillustrated with the schematic top view shown in FIG. 3. This embodimentis a further folded version of the embodiment of FIGS. 1A-1C, shown as asolid glass embodiment that uses a concave reflector 40 in place of lens20 of FIGS. 1A-1C or lenses 20 a and 20 b of FIGS. 2A-2B. Light enteringthe wavelength router 10″ from input port 12 forms diverging beam 18,which includes the different spectral bands. Beam 18 encounters concavereflector 40, which collimates the light and directs it to reflectivediffraction grating 25, where it is dispersed so that collimated beamsat different wavelengths are directed at different angles back towardsconcave reflector 40. Two such beams are shown explicitly, one in solidlines and one in dashed lines. The beams then encounter retroreflectors30 and proceed on a return path, encountering concave reflector 40,reflective grating 25′, and concave reflector 40, the final encounterwith which focuses the beams to the desired output ports.

3. Optical-Switch Retroreflector Implementations

FIG. 4A shows schematically the operation of a retroreflector,designated 30 a, that uses two-position micromirror optical switches(sometimes called “1×2 optical switches”). FIG. 4B is a top view. A pairof micromirror arrays 62 and 63 is mounted to the sloped faces of aV-block 64. A single micromirror 65 in micromirror array 62 and a row ofmicromirrors 66(1 . . . M) in micromirror array 63 define a singleretroreflector. Micromirror arrays may conveniently be referred to asthe input and output micromirror arrays, with the understanding thatlight paths are reversible. The left portion of the figure showsmicromirror 65 in a first orientation so as to direct the incoming beamto micromirror 66(1), which is oriented 90° with respect to micromirror65's first orientation to direct the beam back in a direction oppositeto the incident direction. The right half of the figure showsmicromirror 65 in a second orientation so as to direct the incident beamto micromirror 66(M). Thus, micromirror 65 is moved to select the outputposition of the beam, while micromirrors 66(1 . . . M) are fixed duringnormal operation. Micromirror 65 and the row of micromirrors 66 (1 . . .M) can be replicated and displaced in a direction perpendicular to theplane of the figure. While micromirror array 62 need only beone-dimensional, it may be convenient to provide additional micromirrorsto provide additional flexibility.

In one embodiment, the micromirror arrays are planar and the V-groovehas a dihedral angle of approximately 90° so that the two micromirrorarrays face each other at 90°. This angle may be varied for a variety ofpurposes by a considerable amount, but an angle of 90° facilitatesrouting the incident beam with relatively small angular displacements ofthe micromirrors. In certain embodiments, the input micromirror arrayhas at least as many rows of micromirrors as there are input ports (ifthere are more than one), and as many columns of mirrors as there arewavelengths that are to be selectably directed toward the outputmicromirror array. Similarly, in some embodiments, the outputmicromirror array has at least as many rows of micromirrors as there areoutput ports, and as many columns of mirrors as there are wavelengthsthat are to be selectably directed to the output ports.

In a system with a magnification factor of one-to-one, the rows ofmicromirrors in the input array are parallel to each other and thecomponent of the spacing from each other along an axis transverse to theincident beam corresponds to the spacing of the input ports. Similarly,the rows of micromirrors in the output array are parallel to each otherand spaced from each other (transversely) by a spacing corresponding tothat between the output ports. In a system with a differentmagnification, the spacing between the rows of mirrors would be adjustedaccordingly.

Embodiments of the invention permit multiposition switching arrangementsin which an optical signal from a signal input fiber may be directed toany of N (>2) output fibers. This is illustrated in FIG. 4C, in whichmicromirror arrays 72 and 73 are mounted to the sloped faces of V-block74. A 1×N optical switch is defined by multiposition micromirror 75 andthe N fixed micromirrors 76. For each of its multiple positions,micromirror 75 directs the optical signal incident from the input portto one of the fixed micromirrors 76, where it is directed to acorresponding output port.

Embodiments of the invention include methods and structures that permitvarious tilted positions of micromirrors. These positions may beachieved by using a pivot on which an individual micromirror is tilted.As used herein, the terms “pivot” and “pivot member” are intended tohave broad meanings. For example, the pivot or pivot member may be aflexure. In some embodiments, the pivot or pivot member may use atorsion-beam or cantilever arrangement. In some embodiments describedbelow, the micromirror is capable of assuming positions which have tiltsin a plurality of directions; the terms accordingly includemultidimensional pivot structures that may provide such tilt positions.The terms also encompass other structural elements that may be used toachieve tilted micromirror positions.

An example is provided in FIGS. 5A and 5B illustrating a particularmicroelectromechanical system (“MEMS”) micromirror structure thatimplements a bipositional micromirror that may be used in the 1×2switch. Each micromirror 116 is mounted on a base 112 that is connectedby a pivot 108 to an underlying structural film 104. Movement of anindividual micromirror 116 is controlled by energizing actuators 124 aand/or 124 b disposed underneath the micromirror 116 on opposite sidesof the pivot 108. Hard stops 120 a and 120 b are provided to stop theaction of the micromirror base 112.

Energizing the actuator 124 a on the left side of the pivot 108 causesthe micromirror 116 to tilt on the pivot 108 towards that side until oneedge of the micromirror base 112 contacts the left hard stop 120 a, asshown in FIG. 5A. Alternatively, the actuator 124 b on the right side ofthe pivot 108 may be energized to cause the micromirror 116 to tilt inthe opposite direction, as shown in FIG. 5B. Sometimes hard stops 120 aand 120 b are not provided so that the micromirror base 112 is in directcontact with the structural film 104. The structure shown may beimplemented as a “torsion-beam” structure, in which the pivot 108comprises two structures on opposite sides of the micromirror base 112(orthogonal to the page), connected with a beam that defines therotation of the micromirror base 112. Alternatively, the structure maybe implemented such that the pivot 108 is a post positionedapproximately at the center of the micromirror base 112.

4. Stepwise Controlled Tilting Micromirrors

Embodiments of the invention provide movable hard stops such that morethan two configurations may be realized with a given micromirror. Thereare various reasons why such an arrangement is beneficial. For example,by using a configuration in which a micromirror has N (>2) possibleconfigurations, a 1×N optical switch may be provided. Accordingly, asdescribed with respect to FIG. 5C above, the 1×N optical switch may beincorporated within a wavelength router so that an optical signal froman input port may be directed to any of N output ports depending on astate of the 1×N optical switch. This permits the wavelength router tofunction with greater versatility and increased bandwidth.

Even in embodiments where the micromirror is to be used as a 1×2 opticalswitch, there are benefits to having an increased number of possibleconfigurations for the micromirror. For example, two of the positions(out of the N available) may be specifically selected to optimizealignment of the micromirror rather than being constrained to twopredetermined positions. Once the two optimized positions are selected,the 1×2 optical switch may be operated by moving the micromirror betweenthe two optimized positions. This optimization may be carried outseparately for each micromirror in a wavelength router, therebyoptimizing the efficiency of the router. Certain of the embodimentsdescribed below permit the micromirror to be positioned inconfigurations that vary in more than a single dimension. Alignmentoptimization with such multidimensional positioning permits, in someembodiments, even greater optimization of each individual micromirror,translating into even greater operational efficiency of a wavelengthrouter into which they may be incorporated.

a. Movable Hard Stop

FIGS. 6A-6E show one embodiment of the invention in which hard stops maybe moved through linear actuation. The micromirror structure, which maybe of the torsion-beam type, includes a base 612 supported by a pivot608 that is connected with a structural film 604. The micromirror 616 isformed with a reflective coating, such as gold, on the base 616. In theillustrated embodiment, two fixed rotational actuators 624 a and 624 bare provided on either side of the pivot 608 to cause rotation of themicromirror base 612 into different configurations. The fixed rotationalactuators 624 a and 624 b may be activated by establishing a potentialdifference V between one of the fixed rotational actuators and themicromirror base. For example, applying a potential difference V to theright fixed rotational actuator 624 b produces an electrostaticattraction with the micromirror base 612 that causes it to tiltdownwards to the right. Similarly, applying a potential difference V tothe left fixed rotational actuator 624 a produces an electrostaticattraction with the micromirror base 612 that causes it to tiltdownwards to the left.

The different micromirror configurations are defined not only by thedirection of rotation as dictated by activation of the fixed rotationalactuators 624 a and 624 b, but also by the position of the movable hardstops 620 a and 620 b, also provided on either side of the pivot 608.The position of each of the movable hard stops 620 a and 620 b may beadjusted through activation of respective linear actuators 622 a and 622b. In the illustrated embodiment, the micromirror arrangement provides,in addition to the neutral horizontal position shown in FIG. 6A, fourdistinct positions for the micromirror 616. This is accomplished withlinear actuators 622 a and 622 b that each permit the respective hardstops 620 a and 620 b to be in one of two positions.

FIGS. 6B and 6C show the operation of the micromirror arrangement whenboth hard stops 620 a and 620 b are positioned laterally outside anorthogonal projection of the micromirror base 612 onto the structuralfilm 604. “Orthogonal” is meant to refer to perpendicularity withrespect to the plane of the structural film. In such a configuration,neither hard stop 620 a nor 620 b will be encountered by the base 612when it rotates upon activation of one of the fixed rotational actuators624 a or 624 b. Thus, the micromirror functions in the same fashion asthe arrangement in FIGS. 5A and 5B, except that the micromirror base 612comes into contact with the substrate 604 when in a rotated position. Inan alternative embodiment, fixed hard stops may additionally be providedso that the micromirror base comes into contact with a fixed hard stopinstead of in direct contact with the structural film 604.

FIGS. 6D and 6E show that two additional configurations for themicromirror arrangement are provided when at least one of the hard stops620 a or 620 b is moved laterally within the orthogonal projection ofthe micromirror base 612 onto the structural film 604 by activation ofthe respective linear actuator 622 a or 622 b. When the right hard stop620 b is moved to its second position by the right linear actuator 622b, and the right fixed rotational actuator 624 b is also activated, asshown in FIG. 6D, the micromirror arrangement has a tilted configurationin which the micromirror base 612 is supported above the structural film604. The corresponding arrangement for a left-tilted micromirrorconfiguration with the micromirror base 612 supported above thestructural film 604 is shown in FIG. 6E. There, the left hard stop 620 ais moved to its second position by the left linear actuator 622 a, andthe left fixed rotational actuator is activated.

It is noted that the micromirror tilts shown in FIGS. 6D and 6E may beachieved with activation of a single linear actuator 622 a or 622 b asappropriate, or by activation of both linear actuators 622 a and 622 b.As such, another arrangement that achieves the same four micromirrorpositions (in addition to the neutral horizontal position shown in FIG.6A) may be achieved with a single linear actuator. One such arrangementis illustrated in FIGS. 7A-7D. In this embodiment, the micromirror base712 is covered with a reflective coating 716 and supported by a pivot708, which is connected with a structural film 724. Fixed rotationalactuators 724 a and 724 b are provided on either side of the pivot 708to cause the micromirror base 712 to tilt to the left or right when theyare activated. Movable hard stops 720 a and 720 b are connected witheach other with connector 723 so that the separation between themremains fixed in each configuration shown in FIGS. 7A-7D. The connectedmovable hard stops 720 a and 720 b are moved by actuation of linearactuator 722, which may provide two positions in the illustratedembodiment.

Thus, when the linear actuator 722 is configured in the first of its twopositions, as shown in FIGS. 7A and 7B, the micromirror may be tilted totwo orientations upon activation of one of the fixed rotationalactuators 724 a or 724 b. The first position may be defined by the factthat the left hard stop 720 a is underneath the micromirror base 712,but the right hard stop 720 b is not. “Underneath” is used in thespecific sense that the left hard stop 720 a is laterally within anorthogonal projection of the micromirror base 712 on the structural film704 and the right hard stop 720 b is laterally outside that projection.Upon activation of fixed rotational actuator 724 b, therefore, themicromirror base 712 tilts to the right such that the base 712 is incontact with the structural film 704. Upon activation of fixedrotational actuator 724 a, the micromirror base 712 tilts to the liftand such that the base 712 is in contact with hard stop 720 a.

The complementary micromirror orientations are shown in FIGS. 7C and 7Dwhere the linear actuator 722 is in the second of its two positions. Inthis position, the right hard stop 720 b is underneath the micromirrorbase, but the left hard stop 720 a is not. Accordingly, when the leftfixed rotational actuator 724 a is activated, as in FIG. 7C, themicromirror is tilted to the left with the micromirror base 712 incontact with the structural film 704. When instead the right fixedrotational actuator 724 b is activated, as in FIG. 7D, the micromirroris tilted to the right with the micromirror base 712 support by theright hard stop 720 b. In an alternative embodiment, fixed hard stopsmay additionally be provided so that in either or both of theconfigurations shown in FIGS. 7A and 7D, the micromirror base 712contacts a fixed hard stop instead of making direct contact with thestructural film 704.

In the single-linear-actuator embodiments, the micromirror assemblyshould be constructed so that the connector 723 does not interfere withoperation of the assembly. There are various ways in which the assemblymay be structured to avoid such interference, one of which is shown inFIG. 7E, which is a top view of a configuration corresponding to FIG.7A, i.e. the micromirror base 712 is tilted to the right with the rightrotational actuator 724 b activated and the linear actuator 722 in thefirst position. Hidden structures are shown in shadow line. In theillustrated embodiment, the pivot is configured as a torsion beam 710supported by two support structures 709 a and 709 b. The micromirrorbase 712 includes notches 714 a and 714 b configured such thatsufficient space is provided for the micromirror base 712 to rotate soas to make contact with the structural film 704 without contacting theconnector 723. With the configuration shown, the notches 714 a and 714 bdo not affect the reflective coating 716 so that the optical propertiesof the micromirror arrangement are unaffected.

In alternative embodiments, different pivot mechanisms for themicromirror base may be used. For example, in one alternativeembodiment, a cantilever-type pivot is provided in which the micromirrorbase is tilted at its side rather than near its middle. For this andother pivot mechanisms, the linearly actuated hard stops may be used toprovide different tilt configurations.

b. Multilevel Movable Hard Stops

In other embodiments, a greater number of micromirror orientations isprovided with multilevel movable hard stops. In one such embodiment, themultilevel movable hard stops are configured with a staircase structure,the number of levels corresponding to the number of stairs in thestaircase. With a movable left hard stop having n_(L) levels and amovable right hard stop having n_(R) levels, the total number ofpossible micromirror orientations is n_(L)+n_(R)+3, including theneutral horizontal orientation and two orientations in which themicromirror base is in contact with the structural film. The number ofpositions for the hard stops should be at least n_(L)+1 and n_(R)+1 toaccommodate all of the available levels. There are various ways in whichthe multilevel hard stops may be configured to stop the rotation of themicromirror base at its different levels. One way is to use linearactuation, as illustrated in FIGS. 8A-8F, although other ways, includingflexure bending and rotation, are also within the scope of theinvention.

FIGS. 8A-8F show cross-sectional views of a micromirror arrangement thatuses multilevel movable hard stops. A reflective coating 816 is providedon a micromirror base 812, which is connected with a structural film 804by pivot 808. Fixed rotational actuators 824 a and 824 b provided oneither side of the pivot 808 provide means for causing the micromirrorbase 812 to tilt into different orientations upon activation. In theillustrated embodiment, movable hard stops 820 a and 820 b, each havingtwo levels, are provided. While the number of levels provided for eachof the hard stops is the same, and they are shown at the same heightabove the structural film 804, the invention is not so restricted. Thehard stops 820 a and 820 b may be configured asymmetrically, withdifferent numbers of levels at different heights. The hard stops 820 aand 820 b are connected with connector 823 and moved simultaneously withlinear actuator 822. In alternative embodiments, the hard stops may bemoved independently with separate actuators so that connector 823 isunneeded.

In the embodiments illustrated in FIGS. 8A-8F, n_(L)=n_(R)=2, so thatthe total number of orientations for the micromirror assembly, includingthe neutral horizontal position, is seven. The number of positions forthe linear actuator 822 is three; this accommodates orientations definedby contact of the micromirror base 812 with the structural film and witheach of the two levels of each hard stop. Thus, FIGS. 8A-8C show theorientations of the micromirror assembly when the right fixed rotationalactuator 824 b is activated for each of the three linear-actuatorpositions. In FIG. 8A, the right hard stop 820 b is not underneath themicromirror base 812, which therefore contacts the structural film 804directly. In FIG. 8B, only the first level 819 b of the right hard stop820 b is underneath the micromirror base 812, so that the base 812therefore is supported by the first level 819 b to produce a differentangle of inclination. In FIG. 8C, the second level 818 b of the righthard stop 820 b is underneath the micromirror base 812, so that still adifferent angle of inclination results from contact between the secondlevel 818 b and the micromirror base 812.

Similarly, FIGS. 8D-8F show the orientation of the micromirror assemblyrespectively for the same three positions of the linear actuator 822 asFIGS. 8A-8C, except that the left fixed rotational actuator 824 a isactivated instead of the right fixed rotational actuator 824 b. Thus, inFIG. 8D, the second level 818 a of the left hard stop 820 a isunderneath the micromirror base 812, and the orientation of themicromirror assembly is defined by contact between the micromirror base812 and the second level 818 a. In FIG. 8E, only the first level 819 aof the left hard stop 819 a is underneath the micromirror base 812 sothat contact between the first level 819 a and the micromirror base 812defines a different orientation. Finally, in FIG. 8F, no part of theright hard stop 820 a is underneath the micromirror base 812 so that afurther orientation results from contact with the structural film 804.

In one alternative embodiment, supplementary hard stops may additionallybe provided so that in one or both of the configurations correspondingto FIGS. 8A and 8F, the micromirror base 812 is in contact with a hardstop instead of with the structural film 804. Such supplementary hardstops may be fixed in position. It will also be appreciated that thenumber of available orientations increases as the movable hard stops 820a and 820 b are provided with additional levels. Furthermore, differentpivot mechanisms for the micromirror base may be used in conjunctionwith the multilevel movable hard stops. For example, in one alternativeembodiment, a cantilever-type pivot is provided in which the micromirrorbase is tilted at its side rather than near its middle.

c. Multidimensional Orientations

The principles of the stepwise control of tilting micromirrors for asingle dimension as described above may be additionally be applied tomultidimensional orientations. Such multidimensional orientations mayprovide significantly greater numbers of possible orientations. Severalexamples of such configurations are provided by FIGS. 9A-9F. Hiddenstructures are shown in shadow line. The basic structure of themicromirror arrangement in those figures is similar to that alreadydiscussed. A micromirror base 912 is pivotally supported above astructural film 904 by a pivot 908, which is shown in the figures as apost pivot. A reflective coating 916 is included on the micromirror base912 to provide the desired optical properties of the micromirrorarrangement.

FIGS. 9A-9F illustrate embodiments providing two-dimensional variationin orientations of micromirror tilts by using movable hard stops 920 ina variety of different positions. For exemplary purposes, the hard stops920 are shown with two levels, although a different number of levels maybe used to provide a different number of available tiltedconfigurations. The micromirror base 912 is shown as square, havingsides 961, 962, 963, and 964, but other shapes may alternatively be usedwith movable hard stops 920 in various two-dimensional combinations toachieve a further variety of possible orientations. While FIGS. 9A-9Fillustrate implementation of hard stops that are movable through linearactuation, it will be appreciated that alternative methods of movement,including flexure bending and rotation, may instead by used.

Each of the embodiments shown in FIGS. 9A-9F uses electrostaticattraction provided by fixed actuators 924 to tilt the micromirror base912 down towards where it may contact one or more of the movable hardstops 912 that may be positioned under the micromirror base 912. Asshown, the examples in FIGS. 9A-9F contemplate that some tiltedorientations will include contact between the micromirror base 912 andthe structural film 904; alternatively, fixed hard stops mayadditionally be provided to avoid such contact. In every instance,configurations tilted along linear combinations of the x and y axes asdefined in the figures are possible.

In each of the embodiments shown, the micromirror base 912 may be tiltedinto a plurality of different tilt positions that define atwo-dimensional space of tilt positions in the following specific sense.For any two tilt positions, a tilt axis may be defined as the axis alongwhich the micromirror base 912 is tilted to move from one of the twotilt positions to the other. According to embodiments of the invention,at least one additional tilt position is provided that cannot be reachedfrom either of those two tilt positions by tilting the micromirror base912 along the tilt axis. Instead, such an additional tilt positionrequires that there at least be a tilt component in a directionorthogonal to the tilt axis.

Thus, in FIG. 9A, three linearly actuated movable hard stops 920 areprovided at three corners of the micromirror base 912. Two of the hardstops 920 are configured to move orthogonal to side 964 and one of thehard stops 920 is configured to move orthogonal to side 962. Fixedactuators 920 are provided at each of the four corners so that variousmay be realized. For example, the micromirror base 912 may be tilted byactivating a single one of the fixed actuators 920. If the activatedfixed actuator is in the one in the upper right corner, only one tiltedposition is possible. If any of the other three fixed actuators isactivated, three tilted positions may be realized by having themicromirror base 912 contact the structural film 904 or one of the twolevels of the movable hard stop 920.

Other tilted positions may be achieved by activating two of the fixedactuators. There are four possible pairings. Two of the pairings involvethe upper right actuator, thereby providing three possible tiltedpositions according to the position of the movable hard stop 920corresponding to the other actuator of the pairing. The other twopairings permit nine tilted positions, the product of three positionsfor each of the two corresponding movable hard stops 920. Thus, thetotal number of positions available for the micromirror assembly,including the neutral horizontal position is 35. If the upper rightfixed actuator is not included, the total number of positions availableis 28.

A variation on the arrangement of FIG. 9A is shown in FIG. 9B. The twomovable hard stops that were configured to be linearly actuatedorthogonal to side 964 are instead configured to be linearly actuatedorthogonal to sides 961 and 962. The tilted orientations available tosuch an arrangement are substantially the same as for the arrangement ofFIG. 9A. Specifically, if the upper right fixed actuator 924 isincluded, there are 35 positions available for the micromirror assembly,including the neutral horizontal position. That number is reduced to 28available positions if the upper right fixed actuator 924 is notincluded.

A further variation that uses three movable hard stops 920 is shown inFIG. 9C. In this instance, one of the hard stops is positionedapproximately midway along an edge of the micromirror base 912 insteadof proximate a corner of the micromirror base 912. Only three fixedactuators 924 are provided, each corresponding to one of the hard stops920 and configured to tilt the micromirror base 912 in a directiontowards such hard stop 920. The micromirror base 912 may be tilted byactivating only one of the fixed actuators 920, each thereby providingthree possible tilted positions depending on the position ofcorresponding movable actuator 920. There are also three possiblepairings where two fixed actuators 920 are activated simultaneously,each providing nine possible tilted positions. Thus, the number oftilted orientations that may be achieved is 37. It is noted that the sixtilted configurations of FIGS. 8A-8F can be achieved by activation ofthe right fixed actuator for the three positions of the right movablehard stop and by simultaneous activation of the pair of left fixedactuators when the left pair of movable hard stops are at the same threelevels.

FIGS. 9D, 9E, and 9F each show configurations in which four movable hardstops 920 are provided, with four corresponding fixed actuators 924configured to tilt the micromirror base 912 in a direction towards thecorresponding movable hard stop 920. In FIGS. 9D and 9E, the fixedactuators 924 and hard stops 920 are provided proximate the corners ofthe micromirror base 912, on only two sides in FIG. 9D but on four sidesin FIG. 9E. In FIG. 9F, the fixed actuators 924 and hard stops 920 areprovided proximate the centers of the sides 961, 962, 963, and 964 ofthe micromirror base 912.

The number of possible micromirror orientations possible by thearrangements of each of FIGS. 9D, 9E, and 9F is the same. Each of thefour fixed actuators 924 may be activated singly, to produce threedifferent tilts depending on the position of the corresponding movablehard stop 920. In addition, stable configurations may result fromactivation of pairs of fixed actuators 924, each such pair producingnine different tilts depending on the positions of the two correspondingmovable hard stops 920. Thus, including the neutral horizontal position,the four-hard-stop configurations of FIGS. 9D, 9E, and 9F permit 49different tilt orientations.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Accordingly, the above description should not be taken aslimiting the scope of the invention, which is defined in the followingclaims.

1. A microstructure for steering light, the microstructure comprising: astructural film; a pivot member connected with the structural film andsupporting a base, the base including a reflective coating; at leastthree noncollinear fixed rotational actuators connected with thestructural film, each such fixed rotational actuator being configured todeflect the base towards the structural film upon activation; and amovable hard stop connected with the structural film, wherein the baseassumes one of a plurality of tilt positions according to which of suchfixed rotational actuators is activated and according to a position ofsuch movable hard stop.
 2. The microstructure recited in claim 1 whereinthe movable hard stop comprises a plurality of discrete levels, each ofwhich contacts the base in one of such plurality of tilt positions. 3.The microstructure recited in claim 1 wherein the movable hard stop islinearly actuated.
 4. The microstructure recited in claim 1 furthercomprising a plurality of noncollinear movable hard stops connected withthe structural film, wherein the base assumes one of a plurality of tiltpositions according to which of such fixed rotational actuators isactivated and according to a position for each of such movable hardstops.
 5. The microstructure recited in claim 4 wherein the number ofmovable hard stops is equal to the number of fixed rotational actuators.6. The microstructure recited in claim 5 wherein a subset of theplurality movable hard stops are configured to move collinearly.
 7. Themicrostructure recited in claim 6 wherein the movable hard stops in thesubset are connected with each other.
 8. The microstructure recited inclaim 4 wherein each movable hard stop comprises a plurality of discretelevels, each of which contacts the base in at least one of suchplurality of tilt positions.
 9. The microstructure recited in claim 8wherein each of such movable hard stops comprises the same number ofdiscrete levels.
 10. The micro structure recited in claim 4 wherein eachof such movable hard stops is linearly actuated.
 11. The microstructurerecited in claim 1 wherein the pivot member comprises a post pivot. 12.The microstructure recited in claim 1 wherein the reflective coatingcomprises gold.
 13. A method for fabricating a microstructure forsteering light, the method comprising: forming a pivot member on astructural film; forming a base on the pivot member; depositing areflective coating on the base; forming at least three noncollinearfixed rotational actuators over the structural film, each such fixedrotational actuator being configured to deflect the base towards thestructural film upon activation; and forming a movable hard stop overthe structural film such that the base may assume a plurality of tiltpositions by activating a selection of such fixed rotational actuatorsand moving the movable hard stop to a desired position.
 14. The methodrecited in claim 13 wherein forming the movable hard stop comprisesforming a plurality of movable hard stops over the structural film suchthat the base may assume a plurality of tilt positions by activating aselection of such fixed rotational actuators and moving the plurality ofmovable hard stops to desired positions.
 15. The method recited in claim14 wherein a subset of the plurality of movable hard stops are connectedwith each other.
 16. The method recited in claim 14 wherein forming theplurality of movable hard stops comprises forming a plurality ofdiscrete levels on at least one of such movable hard stops, wherein eachof the discrete levels is configured to contact the base in at least oneof such plurality of tilt positions.
 17. The method recited in claim 14wherein forming the plurality of movable hard stops comprising forming aplurality of discrete levels on each movable hard stop, wherein each ofthe discrete levels is configured to contact the base in at least one ofsuch plurality of tilt positions.
 18. The method recited in claim 13wherein forming the pivot member comprises forming a post pivot.
 19. Amethod for steering light from an input port to one of a plurality ofoutput ports, the method comprising: tilting a micromirror assemblyamong at least three tilt positions that correspond to three of theoutput ports, wherein a first and second of such at least three tiltpositions define a tilt axis and a third of such at least three tiltpositions includes a tilt component orthogonal to the tilt axis, andwherein tilting the micromirror assembly comprises moving a movable hardstop; and reflecting light provided by such input port off themicromirror assembly to such one output port.
 20. The method recited inclaim 19 wherein tilting the micromirror assembly comprises moving aplurality of movable hard stops.
 21. The method recited in claim 20wherein at least one of the plurality of movable hard stops includes aplurality of discrete levels.
 22. A method for defining alignment of aplurality of micromirror assemblies between input and output portscomprising, for each such micromirror assembly: tilting the micromirrorassembly to at least three different tilt positions, at least one ofwhich has a tilt component orthogonal to a tilt axis defined by anotherpair of such tilt positions; measuring an alignment acceptability foreach such tilt position; and determining which of such positionsprovides the greatest alignment acceptability.
 23. The method recited inclaim 22 wherein tilting the micromirror assembly comprises moving ahard stop.
 24. The method recited in claim 22 wherein tilting themicromirror assembly comprises moving a plurality of movable hard stops.25. The method recited in claim 24 wherein at least one of the pluralityof movable hard stops includes a plurality of discrete levels.
 26. Amicrostructure for steering light, the microstructure comprising;support means; micromirror means connected with the support means andtiltable to at least three tilt positions, wherein a first and second ofsuch at least three tilt positions define a tilt axis and a third ofsuch at least three tilt positions includes a tilt component orthogonalto the tilt axis, and wherein the micromirror means comprises movablehard stop means connected with the support means to define the at leastthree tilt positions.
 27. The microstructure recited in claim 26 whereinthe micromirror means comprises a plurality of movable stop meansconnected with the support means to define the at least three tiltpositions.
 28. The microstructure recited in claim 27 wherein at leastone of the plurality of movable stop means comprises a plurality ofdiscrete levels, each of which corresponds with one of the at leastthree tilt positions.
 29. A wavelength router for receiving, at an inputport, light having a plurality of spectral bands and directing subsetsof the spectral bands to respective ones of a plurality of output ports,the wavelength router comprising: a free-space optical train disposedbetween the input port and the output ports providing optical paths forrouting the spectral bands, the optical train including a dispersiveelement disposed to intercept light traveling from the input port; and arouting mechanism having at least one dynamically configurable routingelement to direct a given spectral band to different output portsdepending on a state of the dynamically configurable routing element,wherein the dynamically configurable routing element includes: amicromirror assembly that includes a base connected with a structuralfilm by a pivot member; at least three noncollinear fixed rotationalactuators connected with the structural film, each such fixed rotationalactuator being configured to deflect the base towards the structuralfilm upon activation; and a movable hard stop connected with thestructural film, wherein the base assumes one of a plurality of tiltpositions according to which of such fixed rotational actuators isactivated and according to a position of such movable hard stop.
 30. Thewavelength router recited in claim 29 wherein the dynamicallyconfigurable routing element includes a plurality of movable hard stopsconnected with the structural film, wherein the base assumes one of aplurality of tilt positions according to which of such fixed rotationalactuators is activated and according to a position for each of suchmovable hard stops.
 31. The wavelength router recited in claim 30wherein at least one of the plurality of movable hard stops includes aplurality of discrete levels, each of which contacts the base in atleast one of such plurality of tilt positions.